Android 4.4 with Selendroid mode, causes [SELENDROID ERR]

Hi folks,

I’m running my test code with Selendroid mode, but always got SELENDROID ERR.
Any suggestion to me?

        DesiredCapabilities cap = new DesiredCapabilities();
        cap.SetCapability(CapabilityType.BrowserName, "");
        cap.SetCapability("appium-version", "1.2");
        cap.SetCapability("platformName", "Android");
        cap.SetCapability("platformVersion", "4.4");
        cap.SetCapability("automationName", "selendroid");
        cap.SetCapability("appPackage", "xxx");
        cap.SetCapability("appActivity", "xxx");
        cap.SetCapability("deviceName", "Nexus 4");
        cap.SetCapability("app", apkPath);

Best Regards,
Lucas Luo